In general, a hydraulic excavator as a construction machine is constituted by a self-propelled lower traveling structure, an upper revolving structure mounted on the lower traveling structure, capable of revolving around a center of a revolving device as a revolving center, and a working mechanism provided on the upper revolving structure, capable of moving upward/downward.
The upper revolving structure is constituted by including a revolving frame forming a support structural body, a counterweight provided on a rear side of the revolving frame and taking a weight balance with the working mechanism, an engine located on a front side of the counterweight and mounted on a rear side of the revolving frame in a horizontal position extending in a left-and-right direction, a cooling fan rotating with the engine as a power source and suctioning an outside air as cooling air, a heat exchanger arranged closer to an upstream side in a flow direction of the cooling air than the cooling fan, and an exterior cover forming a machine chamber accommodating onboard devices such as the engine, the heat exchanger and the like on the revolving frame.
For the engine of the hydraulic excavator, a diesel engine is used, and this diesel engine discharges nitrogen oxides (hereinafter referred to as NOx) together with the exhaust gas. Thus, an exhaust gas purifying device for purifying NOx contained in the exhaust gas is known. This exhaust gas purifying device is provided in an exhaust pipe of the engine, for example, constituted by a urea selective reduction catalyst for removing nitrogen oxide in the exhaust gas and a urea water injection valve for injecting a urea solution as a reducing agent to the urea selective reduction catalyst and decomposes NOx into a harmless nitrogen gas and water. Thus, a urea water tank for storing the urea water which is a reducing agent and a urea water supply line for supplying the urea water to the urea water injection valve are provided in the hydraulic excavator.
Here, if the urea water (32.5% urea water, for example) used for purifying NOx is held at a high temperature of approximately 60° C., its quality deteriorates in approximately one week and cannot be used anymore, and the higher the temperature becomes, the faster the quality deteriorates. Since the deteriorated urea water has high corrosiveness, there is nonconformity that it corrodes metal components such as the urea water injection valve. Thus, the urea water tank storing the urea water and the urea water supply line through which the urea water flows needs to be arranged at a place where it is hardly susceptible to heat from the engine and a temperature is held low in the machine room.
On the other hand, an art of cooling the urea water in the urea water tank by the cooling air with a low temperature before passing through the heat exchanger by arranging the urea water tank on an upstream side from the heat exchanger in the flow direction of the cooling air is disclosed (Patent Document 1).
Moreover, an art in which a box-shaped or frame-shaped fixing member is fixed to the upper revolving structure, and the urea water tank is arranged inside this fixing member through a heat insulating material is disclosed. As a result, even if the temperature in the machine room is raised by the heat generated by the engine or the like, a temperature rise of the urea water stored in the urea water tank can be suppressed (Patent Document 2).
On the other hand, by laying out the urea water supply line at a position separated from the onboard device which becomes a heat source such as an engine, a hydraulic pump or the like or by covering the urea water supply line with the heat insulating material, a rise of the temperature of the urea water flowing through the urea water supply line can be suppressed.